1. Field of the Invention
The present invention relates to fabrication of photovoltaic cells, more specifically, a surface texture process for fabrication of photovoltaic cells.
2. Description of the Background Art
Solar cells are photovoltaic devices that convert sunlight directly into electrical power. PV or solar cells typically have one or more p-n junctions. Each junction comprises two different regions within a semiconductor material where one side is denoted as the p-type region and the other as the n-type region. When the p-n junction of the PV cell is exposed to sunlight (consisting of energy from photons), the sunlight is directly converted to electricity through the PV effect. PV solar cells generate a specific amount of electric power and cells are tiled into modules sized to deliver the desired amount of system power. PV modules are joined into panels with specific frames and connectors.
The solar cells are commonly formed on a silicon substrate, which may be in form of single or multicrystalline silicon substrates. In practice, it is desired that incident light transmitted into the solar cell efficient converts as such as the optical energy to electrical energy as possible. However, since sunlight may be scattered, refracted, diffracted, or reflected during transmission, there is insufficient light flux for direct conversion to be cost effective.
Accordingly, several different techniques have been developed to enhance light trapping in the solar cells to improve conversion efficiency. For example, different coatings may be applied to the substrate surface to minimize surface reflectance, thereby allowing a higher percentage of incident light to enter in the solar cells, as opposed to being reflecting away from the solar cell. Alternatively, a surface texture may be provided to increase the surface roughness, thereby assisting the light to be trapped and confined in the solar cell. Conventional surface texturing process often utilizes alcohol related compounds as a chemical source for substrate surface treatment. However, alcohol related compounds are flammable, which are fire hazard and be in environmental safety concern, thereby requiring special safety measures during processing. Also, alcohols evaporate at the temperatures needed to assure that the chemical activity of the etchants in the texturing solution is in an optimum range to effectively perform the texturing process. Evaporation of the alcohol components from the texturing bath thus leads to an unstable texturing bath composition when the processes are run at these elevated temperatures.
Therefore, there is a need for an improved surface texture process for solar cell fabrication process.